Is it a spaceship? No, it's a secret US spy plane!

It is the stuff of conspiracy theorists' dreams. A top secret, hypersonic, spy plane was flown by the U.S. in UK airspace without permission. People reported seeing UFO's and documents released suggest the MoD took the rumours seriously. Its investigations threatened to strain the U.S.-British relations. The U.S. has never confirmed the existence of the aircraft, called Aurora. It is rumoured to be capable of flying at mach 8 and can reach any destination in three hours.